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We plan to install 2 open fermenters in our new brewery. We will likely start with 4 fermenters total. We also will have some conditioning/bright tanks as well. My reasoning for the open top is accessibility for doing some "different" beers in the open tanks vs the closed tanks. I like the idea of having NO PRESSURE for these particular beers and as a benefit... these tanks will be a bit cheaper than the top may closed vessels. I have designed these tanks with a local fabricator and will have hinged lids over the top.

The couple questions I keep asking myself are:

-CIP? Well.. I will have a pipe designed similar to a closed tank and I will have a hinged lid where it will go through the middle to the sprayball.

-CylindroConical? Due to using a fairly no floc yeast.. I wonder if it matters to have a 60 degree cone? I may be able to top crop, so what do people think?

Open fermentation is fine for many types of ale that are not packaged but drunk fresh. You are absolutely going to get some foreign critters so packaging is not an option without pasteurisation or sterile filtration.

If the vessels aren't jacketed, then low, wide ones are good for managing temp without refrigeration, but in that case you might want to stick to beer types where a warmer fermentation is customary. Of course, the greater surface area means you'll be inviting more strangers to the party, and the warmer temp means they'll be better served.

IMHO, grain dust is the chief source of heavy infection so the location has to be right. Ideally, you want a clean area with good ventilation, reasonably fresh paint on the walls and ceiling, fairly cool, very little dust, etc.

Fairly high hop & pitch rates, and a reasonably low wort pH -- say around 4.8 - 5.2 to start -- will help fight off undesirable bugs. A temp toward the low end of what your yeast prefer is best, as many bacteria slow down significantly at cooler temps that yeast find perfectly accommodating.

There is going to be some (probably slight) lactic acid production after yeast activity slows. Lower temps will retard it; higher temps will encourage it. Above 10-15 IBU, hops are quite toxic to many bacteria, but not all. Depending on the type of beer, lactic bugs can be a problem or a blessing.

Will the beer be drunk before the acidity becomes unpleasant? That depends on your sanitary practices, ferm and conditioning temps, hop rate, and how fast the beer is consumed. No matter what, the flavour is going to change over time. Usually quite subtly, but the more time, the more change. Some people find this very frustrating. Others find it rather cool.

You can encounter aesthetic issues: pediococcus are not much bothered by hops and can produce a pellicle, and sometimes rope. Fortunately, rather slowly.

Remember that beer so fermented has the potential to contaminate any surface it comes in contact with. This could be a source of headaches in keeping other product sanitary.

Keep in mind also that re-pitching from open fermenters is highly problematic. I would not trust sediment from a CC cone after an open fermentation. Barm off the top, at the height of fermentation, is best. Scrape the surface layer away -- very gently so as not to deflate the barm -- and discard it. Crop the layer below. IMHO, this is the cleanest yeast that an open fermenter is likely to offer at any point.

What about air managment? If you decide to go with an open fermenter, some plan has to be in play with the air and employees, right? I really am asking.
What air purifier would you use, what micron of filtration, and for what size room?

Open fermentation is fine for many types of ale that are not packaged but drunk fresh. You are absolutely going to get some foreign critters so packaging is not an option without pasteurisation or sterile filtration.

We use opens here, but keep them in a positive pressure room with HEPA filtered air piped into it. So yes, you can open ferment and keep a microbiologically stable beer if you've got the beans to spend.

I'll also add, watching your beer ferment away right in front of you never grows old

We use opens here, but keep them in a positive pressure room with HEPA filtered air piped into it.

I hate you

OK, more specifically: I do it without an air purifier, just two 24x24x4 furnace filters rated for 10 µm for the 2 inlets (from outdoors) and a fan in each of 2 windows blowing out. The room is not airtight but it is snugly fitted and sealed with weatherstripping, spray foam, etc.

Unless you can go the deluxe route that kai describes, in the slum version the goal is not to catch microbes, but to catch most of the particles that they hitch rides on.

As for employees, I assume you mean in terms of safety? If you have any doubts about CO2 buildup and employee safety, an O2 depletion monitor/alarm is worth looking into. At a minimum, you should keep the room locked and distribute keys only among ones you know appreciate the potential danger.

For personal cleanliness, I keep a few cotton lab coats hanging up near the door. They never leave the room. Hairnets go without saying.

My room is ~5500m3, so rather small. The fans move 1200m3/h each, and cost about €450 each. Because I'm in the city, I have to replace the filters bi-weekly. They cost me €14 each in bulk. Naturally, YMMV.

Coolest thing I ever saw in a Brewery was Bigfoot sloshing great gobs of yeast over the top of the open fermenter at Sierra Nevada! The sight and smell was unforgettable!
The Latest New Brewer has an article about a German brewery that uses new style open ferms with some pics.

The open fermenters at Kai's brewery are made by Gresser in Germany and come complete with stainless steel floor, sub-floor yeast tanks and crane mounted CIP dome. Nice kit. For pictures, check out the brewery web pages for New Glarus, Ayinger and White Rabbit as well as the manufacturer's web page.

OK, more specifically: I do it without an air purifier, just two 24x24x4 furnace filters rated for 10 µm for the 2 inlets (from outdoors) and a fan in each of 2 windows blowing out. The room is not airtight but it is snugly fitted and sealed with weatherstripping, spray foam, etc.

Unless you can go the deluxe route that kai describes, in the slum version the goal is not to catch microbes, but to catch most of the particles that they hitch rides on.

As for employees, I assume you mean in terms of safety? If you have any doubts about CO2 buildup and employee safety, an O2 depletion monitor/alarm is worth looking into. At a minimum, you should keep the room locked and distribute keys only among ones you know appreciate the potential danger.

For personal cleanliness, I keep a few cotton lab coats hanging up near the door. They never leave the room. Hairnets go without saying.

My room is ~5500m3, so rather small. The fans move 1200m3/h each, and cost about €450 each. Because I'm in the city, I have to replace the filters bi-weekly. They cost me €14 each in bulk. Naturally, YMMV.

Wouldnt the fan disturb the air more? Kind of like stirring the soup.
Does anyone have a name or model number for the air purifiers?
Thanks

The air is going to be dirty, even if you filter it. You track in microbes when you walk in. You bring in dirty air when you open the door. You shed skin. Your drains can very very easily end up dirty. If you want to know what's in your fermentation room, leave a petri dish out for a couple hours, seal it up and see what grows. It appears scary. You can try to limit this, but you can never contain it completely. Try to limit it, but know you're never going to be able to unless it's an actual clean room where you must wear a sanitized suit before going in.

Your krausen on top is what saves you. A single cell of this or that isn't going to get very far competing with billions of yeast cells. If it gets in the beer it needs to replicate and it's going to take it a while in anaerobic conditions. Your biggest risk of bacterial growth isn't in your first generation, it's in your later generations.

Re-propagate often. We go every 3 weeks.

Go with a conical cone. Trub dumps, dry hop dumps, yeast dumps during transfers. You want to be able to get what's at the bottom out and a cone is the best way to do that.

We have a CIP arm that we attach to a port on the tank when we want to CIP, otherwise we have a stainless end that covers the port. We cover the vessel with a sheet of durable canvas.

You can package, both in kegs and bottles. Statistically you're going to get a bottle every now and again that has an anaerobic bacteria in it that will make it sour and gush. You were going to get that bottling with any machine that doesn't cost $100k. Does the beer change? Yes. Does all craft beer change, a lot, over even a three month period in a bottle? Yes. Hell, dry hop aroma rarely can make it a month if you store it cold.

For yeast cropping, you want to do it on day three or four. It's a mix of beer and yeast, if you do it too soon you'll end up with a lot of beer for your next pitch. If you crop too late you won't be able to get anything. Also if you don't get it cold enough it will die, and quickly. It hasn't gone dormant like bottom cropped yeast. Going dormant requires energy and if the yeast uses up everything because the population is higher than the available resources, then they will die in the active state.

When you top crop yeast you take active cells out of fermentation. If you crop out too much, you can stall out your fermentation.

If you have any more questions let me know. Most of what I know is by experience, but I'm willing to share.

Excellent information snowboarder. Can you explain the rest of your process and whether you have any special concerns about oxygenation? What if the beer needs a considerable amount of time to finish? Is there a sufficient layer of CO2 that you can trust and for how long?

When you crop the yeast, how cold do you store it and for how long are you able to store it?

I know these are elementary questions, but I've never done an open fermentation before but am very interested in it for certain styles. Thanks.

Don't worry, I'm still in the process of dialing everything in. I've wanted to talk to other open top fermenter people for a while.

We couldn't get it cold enough with any of our cold rooms, so we store it at 40 F for 3 days max. We fill stainless steel buckets about half way full otherwise it overflows. I also try and take a small sample and put it in our fridge which is right around 32. It allows me to see how much of my slurry is yeast and how much is beer. Three days storage as you can imagine forces us to brew pretty often so we're usually brewing at least 3 days a week.

Another item I didn't mention was cropping and pitching same day. When you do that, the yeast is still in the active state and it gets going a whole lot faster than yeast that has been dormant. Our most explosive fermentations have been pitching the same amount of active yeast as we have dormant yeast. Yeast cell counts were way off the charts compared to the same volume of dormant.

As far as the oxidative stability goes, we're working on it. We do put a little bit of CO2 on the top occasionally both for oxidative stability and to try and prevent any aerobic bacteria that may have dropped in a chance to survive. We don't usually keep the beer in tank any longer than we have to. 7-8 day fermentation, 2 day chill with finings, transfer out.

The direction we're moving is to follow a more traditional English process where we do primary fermentation (first three days) in the open fermenters and then transfer to closed Uni tanks for secondary fermentation and natural build up of CO2. The real advantage is that we'll be able to get usable yeast out of the tank before we dry hop so the next pitch yeast doesn't have hop matter in it.

Another interesting one for you to think about, we brew a variety of different beers with different yeasts. We've had 2 ale strains, a couple belgian strains, a kolsch strain, a bavarian hef strain and a champagne strain all fermenting in different tanks at the same time. No off flavors in any of the beers.